Grit blasting apparatus and the like



J. A. SARG-ROVE GRIT BLASTING APPARATUS II-AND THE LIKE 2 Sheets-Sheet 1 Filed Feb. 25, 1948 FQ, w a

Patented Aug. 29, 1950' GRIT BLASTIN G APPARATUS AND THE LIKE John Adolph Sargrove, Middlesex, England, as

signor of one-half to Sargrove Electronics Limited, Middlesex, England, a British company Application February 25, 1948, Serial No. 10,701 In Great Britain. February 19, 1947 Section 1, Public Law 690, August 8, 1946 Patent expires February 19, 1967 Claims.

This invention relates to apparatus for clean- I ing or abrading by means of projected particles of grit such as sand, carborundum or other abrasive material. The invention relates more particularly but not exclusively to a process in which such apparatus is controlled automatically, and has for its primary object to provide an improved form of apparatus of this kind. The invention is however applicable to other systems in which suction is used to convey granular or pulverulent material.

According to one feature of the invention a Venturi or like suction device is used to suck a supply of abrasive or granular or pulverulent material from a hopper or the like, for delivery to another point, which in the case of a grit blaster may be a projector nozzle or jet and means are provided responsive to the pressure existing in the supply path between the hopper and the suction device for indicating and/or controlling the supply of material. I

According to another feature of the invention, in a grit blasting machine of the type referred to, grit which has been projected from the projector nozzle or jet is collected by means of a hopper or the like disposed beneath the articles which States patent application Serial No. 549,770, filed August 16, 1944, now Patent No. 2,474,988. In this process moulded panels or plates of thermosetting insulating material are sprayed by a metallising process to deposit in and upon depressions in the plate a suitable metallic coating,

which thereby forms components of the apparatus together with interconnecting leads. In carrying out this process however it has been found that if good adherence of the sprayed coating.

to the insulating back is to be obtained it is necessary to give to the normally highly polished surface of the plates a degree of roughness, and for this purpose grit blasting is very suitable.

In carrying out the process of the earlier speeification it is desirable that the successive stages of manufacture should be as automatic as possi ble, so as to require a minimum of human supervision or handling, since the costs of manufacture are substantially increased thereby. At the same time it is equally important that should any stage of a fully automatic process cease to function properly an alarm circuit and/or a stop device be operated, in order that the number of reject articles be minimised.

This invention is therefore primarily concerned with an arrangement which is applicable to a grit blasting apparatus, which, while suitable for the process referred to, is also suitable for other applications in which an automatic supervision and/or indicator device is required.

In the accompanying drawings there is illustrated by way of example an embodiment of the invention which is suitable for incorporation in a fully automatic apparatus certain component stages of which are described and shown in my co-pending United States applications Ser. No. 8,042 filed February 13, 1948, and No, 10,702 filed February 25, 1948. In these drawings Figure 1 is aschematic diagram showing the arrangement of the grit blasting stage as a Whole; Figure 2 is a diagrammatic plan view of the machine; Figure 3 is an elevational view of the apparatus of Figure 2 and Figure 4 is a sectional view through one of the spraying nozzles.

Referring first to Figure 1, which shows the general control arrangement of the complete stage, the stage comprises a conveyor lll adapted to transport past the spraying nozzles H the panels which are to be grit-blasted. The various parts of the stage are under the control of a main control unit [3; this unit has a number of input terminals Sense which respond to conditions in the apparatus and a number of terminals Actuate by which functions are performed. One of the Sense terminals is connected to a presence detector M which may be a trolley switch, photo-electric cell or the like, and which is arranged to respond to the presence of a panel presented to the apparatus. In response to an indication given by the detector [4 the control unit I3 is arranged to energise an electric motor l5 which drives the conveyor Hi. In this way, the conveyor is automatically started when a panel is offered the machine. The conditions of operation of the nozzles I I are extremely arduous, and

it therefore is desirable that they should be used only when a panel is in position in front of the nozzles and ready to be sprayed. There is accordingly provided a second presence detector I6 arranged immediately in front of the spraying station; this second detector, like the first, is connected to the control unit I3 and in response to an indication by the second detector the control unit supplies air under pressure to the sprayis applied to them suction is created by a Venturi 7 action, and this suction is empioyedto drewinto the nozzle the grit which is to be projected against the panels. The grit is supplied to the nozzles 7 over a conduit 19 from a hopper ZO'arranged beneath the nozzles; after being once used the grit falls back into the hopper ah-dthe-siippiy or grit is thus maintained.

To ensure that the panels are uniformly-sub jected to the grit blast the nozzles are oscillated in the vertical plane and with this object the control unit is arranged to energise an electric motor fil hy which through a, suitable rnechanit'ai ee eehhe this osc llation is produced; Pur ther, the controi'um it air-ranged to 'enei'gise "an electric motoriz drivin a-suitabieefir exhaust which serveste-draw off air 'iroin-l-Ihe enciesure in which the -ntiiiastiii'g akes piece, and time prevents the escape o'f grit "to the surroundihg speee.

he up'ply'er eri'tffreih the {hepeei to the sprayv i'flghdzzles is ei'rectea soieiy the suction pro:-

"decent-y the Venturiaction 'of the nozzle; and

ordinarily thegrit 'n'ius'tb'e inaintaitfed in a very coniifbn' ifchoking' er packing is hot to of-pear either in the hepperits-eii or in theeoiicuit fishettir eh hopper an-cl nozzle. 7 such-choking restrts ii -the tenets not being reheat abraded,

ahu it is ther 'rere necessar to plbvide sbrnieind i 'eatioh'fer this failure. one method or uetectihg birch 'lail'ure'it by means of a photoelectric examirration ofth'e processed panel; ifthe surface "g'los's df the" panel incompletely remevedith'e 1' xamination d-evi-e-efm n t the een'troi unit it ty, 9. hontr'oll-in'e' 23; Such an eiarniha' tie vice rnlist or; me as teacher the semi,

tea-h the Whole an lace, is te ee-subsequently inetalli'se'd; thepan' el "is there'forescani'iedfor eitairhple suitable 'rela ve motion of panel and that en, "or by electrical scanning ine'ans;

such enotoeledtric examinationsatctortthatiteanbearranged to-tieteet any defects the 'ahraiied'panei, it has the u'isardvane ftage that it "detects only a'pane'l which is a r'ej'e'o't panel; itis'd'esirabie that ther'esh'oulflbea h roht to "he device'whkh will tie'tect eoniiti'ons which wi i g'iv'e rise to defective pr cessing,

By one feature or the present invention, means are provided to monitor the flow of grit to-t'ne 'hoz'zle'sfandthis is done by 'iiieans'o'f a vacuum v auge "211 which indicates the pressure existing in the'cohdui't [9 between the'hopp'e'r and 'the'n'o'zzle. W11 n the nozzles are "functioning "correctly there will tea vacuum pressure in the conduit which will be indicated by thefg'auge "iii. "If, "however, packin of the it should occur in the hopper er in the conduit between the hopper and the gauge the vacuum fpressureindicated the gauge will increase and hyprdvi'ding an electric contact "'25 upon the gauge which is operatedwhen the pressure rises above the normal range, indication an be given to the 'cohtreninit is. The control unit'eah'theh be arr'eheeii to shut 'deivnthe grit blasting stage even "while processed Ih'il'ililalr 'h'ia Lniier, if the supply of grit "in'the a :pehei is stillb'eing hop er shoul for any reason become exhausted, I V oi'ifteh'okin' should 'oc'ciir in'the niiz'zre's orth the it i'lar 'h'opp'e'rs '21fwhich"cover'substanti'ally tliejen 4 conduit between the nozzles and the gauge, or if the air supply to the nozzle inlet should fail, the vacuum indicated by the gauge will fall and in this case contacts 26 on the gauge are operated, anu give an indication-tome control unit l3 as before." 7

The control unit l3 may also be arranged to attempt remedial action in the event of a fault occurring. The most likely fault to occur in practice is packing of the grit in the base of the hopper :or'inthe conduit 19; and the control unit is therefore arranged to operate one or more vibrator devices 21 which are connected. to flexible portiohs'of the conduit [9. In response to actuation of contacts 25 or 26 the control unit may then Vibrate the conduits in an endeavour to clear the ramtanei then to stop the grit blasting stage only if thefault persists.

The control unit l3- may also be interlocked with thesucceeding stages of the complete machine, tor example over a further control line I "stages 'of'th'e cempiete machine. In common with theoth'er stages, the grit blaster is built in a'se- V riesof similar cubiclesBfi;-3i 32, through the'ce'ntrey'or which runs a conveyor line corresponding toth'e conveyor l0 of Figure 1. This conveyor 1in'e"c6mprises upp'rail'fillfiw'el'b1tS 33,-3 'TBSIZE C tively mounted on pairs "of belt pulleys 35, 3 6, of w i ch'some are driven bythernotor l5. o'elts 3}, '34 "are of rubber, 'or-"siniiiar material, to "res'i'st abrasion by thegri't, ahii'aieoi channel seeti'onto receive and support the" panels such as 31; lretween-theinner spans orthe belts;

In enter that the conveyor inay accommodate pane-is of different vertical heights the upper conveyertelt may heady stable. With this-object the --pu1ieys "at are cani'eeru h hafts mounted in a pair of cross-arms Soho-Id in-horizontallyspared relation; and carried upon four Vertical support 39 whi-ehprojeet through thetop of pubicle'tl,fand"are joined bya head plate' ltl. The heau mate is engaged-"at its 'c'entre'by an adjusting screw M carrying ahead wheel =52 and bearing in a threaded boss; nots'hewn; in the top "o'fthe" clibicle 3i. By this rnean's the complete assembl comprising puiieys at and the "various nieihberstt; 3tahdat" can he "vertically adjustedby the handwhee tt. V V v also mounted in the cubi'cleStaIethespra-ying nozzles 11; both sidesof e'a'oh'p'ane'l-is grit blasted "simultaneously, and the nozzles are theref'or'earranged' ingroupsonoppositesides-er heeonveyor line. As shown iniFigure's '2'anl 3' twonezzies are used 'in'each group; arranged 'at -different a'ngies to the tram dr'the panels so as to secure complete abrasion, "but different number ernez: zl'es may be usedaspirctimstances require.

group-of'noz'zles is car'fied near the lower extremity "of a f-vert'i'caiiy' reciprocating shaft 43'; 'theseshafts areeach carried in two sets of tour "rollers we 'carried on suitable e'ross-inembers, not "sihow'n' in the C1'ibicl'e if! or infion' the-taper th' oubicl'e. These shafts are re'ciprocate'd by two arins lfi having thereinslots engaging ,pinstt on the shaft's-" w'; the ems- 4t "are "pivoted at their ends at n and bear against'th'esurfaces or came "48 drive-hey an electric metorzl. v In this wa'ytheshafts 43 "are 'rec'ipro'cated, and the extent "of their movement "can be controlled by ad, just'rnent offpivot QT.

Beneet the nozzles Hiai'earranged twosinrtire area of the lower part of the cubicles 30, 3i and 32. After spraying however, the grit falls for the most part downwardly within the confines of cubicle 3|, and is thus arranged to fall upon electric panel heaters 49 secured upon the hopper walls. It is found that by arranging that the grit is warmed in this way its fluidity is maintained to a high degree; as a result, the occurrence of packing or choking of the grit is very substantially reduced and the reliability of the apparatus much improved.

The grit, thus maintained fluid, falls to the bottom of the hopper, where. it is drawn ofi through conduits l9 to the respective nozzles l i. When air is applied to the air supply conduits I8 of the nozzles, the necessary suction is created in the conduits l9 .and the grit is picked up. Vacuum gauges 24 are included in the conduits l9, and are fitted with contacts as described above, and vibrators 21 are coupled to the conduits at suitable points.

To start the apparatus, panels are loaded by hand into guides 59 and are pushed past the detector I4 whereupon the main conveyor is started and also a subsidiary conveyor comprising belts 5!, 52 on pulleys 53, 54, driven by a motor 55. An air exhaust fan is also started to draw ofi air from the cubicles through a vent 56.

The now moving conveyor belts 33, accept the panel and transport it, eventually passing the panel through a rubber sealing curtain 57 into the central cubicle. As it enters the cubicle the panel operates the detector and the nozzles are brought into operation, whilst being vertically oscillated. After a predetermined time interval the grit blast is stopped (unless a second panel is closely following) and the panel passes through a second rubber curtain 58 into a small chamber where, by means of a series of powerful air jets 99 the panel is cleaned of grit particles which may still be adhering thereto. The panel then passes through a further curtain 6| onto conveyor belts 5!, 52 and thence to succeeding stages of the apparatus. The separate conveyor formed by belts 5|, 52, is used to avoid carry-over of grit, which would cause excessive wear.

The walls of the cubicle 31 are lined internally with rubber to reduce abrasion by stray grit, and as much of the internal mechanism as possible is similarly protected.

Figure l shows one form of nozzle which has been found satisfactory in use. This nozzle comprises a body 19 of square or round cross section and bored with an opening throughout its length. At the one end of this boring is inserted, either as a force fit or a screw fitting, a replaceable nozzle member H having a tapered boring therein. Screwed into the other end of the opening in the body 10 is a plug 12 having a central jet boring 13 communicating with a series of radial passages 14. The plug and the boring in the body are so shaped that when in position they define two separate chambers to which access is permitted through inlets l8, [9 respectively. When air is applied to inlet l8, a jet is directed into the nozzle opening creating suction on the inlet I9.

The nozzle unit H is subject to rapid wear,

6 and is therefore made of material having a resistance to abrasion as high as possible.

I claim:

1. An automatic grit blasting machine comprising a conveyor for articles to be grit blasted, means for starting said conveyor on presentation to the machine of an article to be grit blasted, means for directing a grit blast against said article and means for starting said grit blast after the starting of said conveyor, a supply of grit and means for feeding said grit to the grit blast means, and means for stopping said grit blast means if the feed of grit thereto is abnormal.

2. A. grit blasting machine, comprising a nozzle through which grit is blasted by air onto an article to be treated, a grit hopper, a conduit extending between said hopper and nozzle for supplying grit to the nozzle, means for supplying air under pressure to said nozzle to create a suction on the grit in said conduit, a vibrator device cooperative with said conduit, and pressure sensitive means responsive to a condition of abnormal pressure in said conduit for putting said vibrator device into operation to thereby vibrate said conduit.

3. A grit blasting machine as defined in claim 2 wherein at least a section of said grit conduit is comprised of flexible material and said vibrator device is operatively associated with said flexible section.

4. A grit blasting machine as defined in claim 2 wherein said pressure sensitive device is constituted by a pressure gauge having electrical contact means thereon adapted to be actuated upon the occurrence of an abnormal pressure condition in said conduit, and said vibrator device is electrically controlled through said contact means.

5. A grit blasting machine comprising a conveyor for articles to be grit blasted, nozzle means disposed laterally of said conveyor for directing a grit blast against the article, means supplying grit to said nozzle, a presence detector arranged adjacent said nozzle for detecting the approach of an. article, means controlled by said detector for starting the grit blast through said nozzle means, and means for stopping said grit blast should the supply of grit to said nozzle means become abnormal.

JOHN ADOLPI-I SARGROVE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 365,261 King et al June 21, 1887 727,930 Tilghrnan May 5, 1993 1,073,149 Lawrence Sept. 16, 1913 1,867,856 McCrery July 19, 1932 1,834,791 McCrery Oct. 25, 1932 2,345,648 'Wolfskill Apr. 4, 1944:

2,431,354 Wallberg Nov. 25, 194:7

' FOREIGN PATENTS Number Country Date 439,982 Great Britain Dec. 18, 1935 

